Disable watchdog some time (minutes) after startup - MPC885

[xaviersoulie]

Hi,

We use equipment based on the MPC885 processor. We want to be able to disable the software watchdog sometime after the software starts. We do not write to the SYPCR register when the device starts. This register is read some time after startup and it is observed that the register contains the default value 0xFFFF FF07. And to prevent the watchdog from being activated, we write in the SWSR register (0x556C and 0xAA39).
We want to deactivate the watchdog according to a command issued by the user of the equipment. When the user asks to deactivate the watchdog we write in the SYPCR register the value 0xFFFF FF88. But unfortunately this is not taken into account. Do we have to perform specific operations before writing to this register.
In the MPC885 reference manual we did not find any indication indicating that this operation is impossible.

Do we have to write to other registers before we can write to this register. This operation will therefore be carried out after having initialized the registers and the drivers.

Knowing that this order is an evolution of our existing equipment. Previously, when the equipment was started, the value 0xFFFF FF88 was written in the SYPCR register and it worked very well. But now we want to be able to disable the watchdog.

We couldn't find any sample code in the site's resources that does this.

Thanks in advance

[yipingwang]

It is clearly described as "written only once after system reset" at the RM.

[xaviersoulie]

Hello yipingwang,
Thank you very much for this answer, so you confirm that I can write at any time in this register after the start.

On the other hand I have the right to write only once in this register.
Have you done this operation before?

Thanks in advance

[yipingwang]

Please refer to the update from the AE team.

MPC885 is a SoC designed more than 20 years ago. All boards at local team has been scrapped due to office shutdown and relocation. Validation needs non-trivial effort.

Most common document error has been discovered and recorded.

Obviously, your customer has violated what the document said.